Method for controlling a drive train

Abstract

A method for operation of a drive train having a drive machine and an automatic, unsynchronized gearwheel variable-speed transmission, which can be connected to the drive machine by using an automatic clutch is described. A control device carries out a selection process as a function of vehicle parameters and/or operating variables of the motor vehicle to determine whether a gear change of the unsynchronized gearwheel variable-speed transmission will be carried out with the clutch engaged or disengaged. To ensure reliable operation of the motor vehicle, a gear change is carried out with the clutch disengaged in a time interval after initial starting up of the drive train and/or after starting of the drive machine and/or when a malfunction is identified in a component in the drive train.

1. A method for controlling a drive train for a motor vehicle, the drive train including a drive machine, an automatic gearwheel variable-speed transmission, an automatic clutch arranged between the drive machine and the gearwheel variable-speed transmission, and a control device, the method comprising:
 the control device making a selection as a function of selection rules and vehicle parameters and variables as to whether the automatic clutch remains engaged or disengaged when a gear change takes place from an original gear to an intended gear in the gearwheel variable-speed transmission; 
 when the gear change is carried out with the clutch engaged, synchronizing a rotation speed of a transmission input shaft to an intended rotation speed in the intended gear by controlling the drive machine; 
 carrying out the gear change exclusively with the clutch disengaged 
 when a malfunction exists in a component of the drive train. 
 
     
     
       2. The method as claimed in  claim 1 , wherein the vehicle parameters vary. 
     
     
       3. The method as claimed in  claim 1 , wherein the gearwheel variable-speed transmission has a synchronization device which is driven by the control device and which is used to brake a transmission input shaft, and wherein in an upshift gear change with the automatic clutch disengaged, the control device selects whether the synchronization device is used to brake the transmission input shaft. 
     
     
       4. The method according to  claim 1 , further comprising:
 carrying out the gear change exclusively with the clutch disengaged when the gear change occurs during a time interval which commences upon an initial starting-up of the drive train and continues until all of the vehicle parameters and variables which are relevant for the selection have been determined by the control device. 
 
     
     
       5. The method as claimed in  claim 1 , further comprising:
 the control device carrying out a test to determine whether the gear change can be carried out with the clutch engaged; and 
 making the selection based on a result of the test. 
 
     
     
       6. The method as claimed in  claim 5 , further comprising carrying out the test as a function of the intended gear for the gearwheel variable-speed transmission. 
     
     
       7. The method as claimed in  claim 5 , further comprising carrying out at least one of the selection and the test in some operating areas as a function of variables which describe at least one of a roadway inclination, a roadway condition, an ambient temperature, a geodetic height and an ambient pressure. 
     
     
       8. The method as claimed in  claim 5 , further comprising carrying out the test as a function of vehicle parameters and variables. 
     
     
       9. The method as claimed in  claim 8 , further comprising carrying out at least one of the selection and the test in some operating areas as a function of the intended gear for the gearwheel variable-speed transmission. 
     
     
       10. The method as claimed in  claim 9 , further comprising carrying out at least one of the selection and the test in some operating areas as a function of variables which describe an environment of the motor vehicle. 
     
     
       11. The method as claimed in  claim 1 , wherein at the start of a downshift gear change, the clutch remains engaged, and the control device
 drives an actuating element to deselect the original gear, 
 determines a time since the driving of the actuating element, 
 monitors whether the original gear has been deselected, and 
 if the determined time exceeds a threshold without the original gear having been deselected, disengages the clutch. 
 
     
     
       12. The method as claimed in  claim 11 , wherein the stated threshold is dependent on at least one of vehicle parameters, vehicle variables, and variables which describe an environment of the motor vehicle.